1. Field of the Invention
The present invention relates generally to devices used for in situ arterial bypass surgery where the operation requires that the valves within the bypass vein be cut and disabled to allow the free flow of blood to the lower extremities.
2. Prior Art
In the field of vascular surgery, the surgeon is sometimes confronted by patients experiencing blood flow problems in the lower extremities. If gone uncorrected, the inevitable result is often tissue death necessitating amputation of the limb. Whether this condition is due to past trauma to the arteries or some other atherosclerotic occlusive disease, a common solution is bypass surgery. Such an operation attempts to bypass the normal functioning of the femoropopliteal arterial system by using one of the saphenous veins as a conduit for arterial bypass surgery. Regardless of the method chosen, the existence of valves in these veins is of major concern.
Because the function of the venous system, as opposed to the arterial system, is to return the deoxygenated blood to the heart and lungs, the venous flow of blood in the lower extremities must overcome the force of gravity to allow blood to reach the heart and lungs and stop the downward flow of blood. To accomplish this, the deep veins of the extremities contain numerous valves which prevent retrograde flow. These valves are actually two semicircular shaped leaflets which are attached to the wall of the vein and are part of the interior endothelial lining of the vessel. When blood is flowing normally, the valves lie close against the vessel wall to allow for circulation. This venous flow of blood is dependent upon the calf muscle pump. With contraction of the deep muscles of the leg, a column of blood is advanced past the next set of valves on the way to the heart and lungs. Consequently, any bypass operation that seeks to use a vein in this area as a substitute conduit for arterial circulation must succeed in eliminating the effect of these venous valves.
One method of arterial bypass is to completely remove a section of the saphenous vein and reverse it to put the open position of the valves in the desired direction of blood flow. While this is a potentially feasible or acceptable technique, it is also a traumatic one. The vein walls are extremely sensitive to handling, lack of blood, and temperature and react to such stimuli by strong contractions resulting in severe venospasms. In addition to damage to the endothelium, the natural tapering of the vessel is transposed and the blood now flows from the narrow end to the larger end. There is evidence that the undesirable turbulent flow characteristics of this arrangement is in some way responsible for the development of intimal hyperplasia reported after such operations.
An alternative to the excision and reversal method of bypass surgery is the rerouting of the vein and disablement of the venous valves in situ, or without dissection of the vein from its natural position. This procedure can be performed through several means, one of which is the use of small scissors inserted through venotomies near the location of the valve to be disabled. The disadvantage of such a method is that many incisions must be made, and visualization of the valve site is necessary to avoid cutting the wall of the vessel or accidentally entering one of the side branches present at all valve sites.
A further alternative is the use of a tool called a valvulotome, sometimes referred to as a Mills cutter. This device is essentially a slightly flexible rod with an orthogonal cutting edge used to make an incision on each leaflet of the valve. A venotomy is performed either on a side branch or on the vein itself, and the valvulotome is inserted into the vessel until it is above the valve in the direction of blood flow. One leaflet is severed by pulling back against the valve, and the device is rotated 180.degree. to sever the other leaflet. As with the scissoring method, the process involves numerous punctures into the vein wall to disable the many valves that may be present. It is also time consuming and requires a high degree of precision to successfully perform the operation due to the possibility of cutting other venous tissue.
Ideally, a venous valve cutter should allow for in situ disablement of the valves without the need for a long incision to expose the entire length of the vein used for bypass circulation. It should be capable of insertion at a distal point of the subject vein and guided easily above the first valve to be cut without danger to the sensitive endothelial lining of the vessel. Such a device should also have a means to allow for use of the valve cutter in a wide range of vein diameter sizes, and should not require any rotation of the device in assuring that each valve is successfully disabled in one pass.